摘要:

During the last decade great attention has been devoted in the technical literature to voltage stability problems of interconnected power systems. However, power system operators have found that voltage collapses often occur in a real system at a load condition different from the one predicted by simulation studies. One of the causes that makes the use of present approaches unreliable is the lack of adequate models for static loads, which are traditionally represented by constant power or, generally, by voltage dependent characteristics. To overcome this difficulty, the paper proposes a new and practical procedure for analysing the effects of static load modelling on the voltage stability limit of power systems. To this purpose an accurate model for static loads is used which takes into account their frequency dependence. This is very important to avoid unacceptable inaccuracies in determining the actual voltage stability limits of heavily loaded and isolated power systems. Two numerical examples illustrate the capability and usefulness of the proposed technique.

DOI:10.1049/ip-c.1993.0001

出版商:IEE    

年代:1993

数据来源: IET

摘要:

A decoupled power flow solution method for well- and ill-conditioned power systems is derived. The proposed method is simple, has no mathematical approximations and requires less storage and computational time than either the Newton-Raphson (NR) method for ill-conditioned systems, or the Fast Decoupled (FD) method for well-conditioned systems. In the derived method, the power flow is decoupled intoPandQpower models without any approximations and thePmodel is decomposed into a generator active power model and a load active power model. The difference between the load active power model matrix and the reactive power model is combined with the mismatch power and the second-order vectors, which enables the same matrix triangulation to be used to solve the load active and load reactive power flow models. The proposed method is adjusted with the optimal multiplier to improve the convergence and decrease the computational time of the ill-conditioned systems. To examine their effectiveness, two ill-conditioned systems, i.e., 11-and 43-bus systems and a well-conditioned 90-node German utility network are studied using the proposed method and compared with the FD and NR methods. The results show that the proposed method has greater computational speed, smaller memory requirements and better convergence than the FD method for well-conditioned systems and gives a convergent solution for ill-conditioned systems while the FD gives a divergent solution.

DOI:10.1049/ip-c.1993.0002

出版商:IEE    

年代:1993

数据来源: IET

摘要:

A robust controller, based on the Riccati-equation approach, is proposed for power system load-frequency control. Only the bounds of the system parameters are required to design the robust load-frequency controller. The proposed robust controller is simple, effective and can ensure that the overall system is asymptotically stable for all admissable uncertainties. Simulation results show that, for the example system, the proposed robust load-frequency controller can achieve good performance even in the presence of generation rate constraint.

DOI:10.1049/ip-c.1993.0003

出版商:IEE    

年代:1993

数据来源: IET

摘要:

A two-stage power system distribution planning algorithm is developed for solving sizing, location and timing problems of distribution substations and primary feeders. This comprehensive algorithm involves an accurate small-area electric load forecasting procedure, and provides the flexibility for both static- and dynamic-planning application modes. Also, the algorithm includes a new nondiscrete planning model which accurately simulates the different cost functions of substations and primary feeders. Moreover, constaints on voltage drop, equipment capacity and power-conservation constraints are included in the planning problem formulation. Finally, the proposed algorithm is illustrated using a detailed numerical example, and subsequently tested for both efficiency and accuracy.

DOI:10.1049/ip-c.1993.0004

出版商:IEE    

年代:1993

数据来源: IET

摘要:

In the standard procedures for high-power short-circuit testing of current-limiting fuses, the test circuit is conventionally characterised by the RMS test voltage, prospective current, frequency, closing angle, and power factor. From these parameters a constantRLequivalent circuit can be derived, which has been widely used in the modelling of fuse-breaking transients, but recent studies have shown that this circuit model is inadequate. The frequency dependence ofRandLhas been investigated by fast-Fourier-transform analysis of fuse-breaking test transients obtained in a high-power short-circuit test laboratory, and the results show that, whileLdecreases slightly,Rincreases greatly with frequency. The nominal-power-factor value provides only a measure of the DC resistance of the circuit. The frequency dependence ofRmust be taken into account for accurate modelling of the operation of current-limiting fuses.

DOI:10.1049/ip-c.1993.0005

出版商:IEE    

年代:1993

数据来源: IET

摘要:

Double-circuit current comparison protection (DCCCP) is an algorithm for travelling-wave-based protection of a double-circuit high-voltage line. It uses the balance between the two circuits to distingush between an internal fault and an external disturbance. To prevent incorrect trips superimposed currents are used, and the relay has to be blocked after detecting an external disturbance. The setting of relay parameters is discussed, as well as its performance. The tripping time is between 100 and 200 μs for the majority of faults. For faults around voltage zero, the tripping time is between 1 and 3 ms, depending on the amplitude of the short-circuit current. Faults close to the remote line terminal are not detected at all. Some direct lightning strokes will lead to an incorrect trip. To overcome the disadvantages of DCCCP, it is combined with travelling-wave-based differential protection in a protective scheme. Differential protection is a somewhat slower but very reliable backup. Its parameter setting is discussed, as well as its performance. The tripping time is between 1 and 3 ms. The protective scheme further contains fast reclosure, breaker-failure detection and adaptive setting for the backup relays.

DOI:10.1049/ip-c.1993.0006

出版商:IEE    

年代:1993

数据来源: IET

摘要:

A mathematical model is presented that accurately predicts the steady-state performance characteristics of three-phase self-excited induction generators operating in parallel and supplying a balanced load. It is shown that it is possible to reduce the (n+1) nonlinear equations which are required in the steady-state analysis of annmachine system, to the solution of only two nonlinear equations. The results show that induction machines with similar or different parameters and speeds can be operated in parallel, and their steady-state performance characteristics can be accurately predicted. The performance characteristics of such machines are influenced by their excitation capacitance, load impedance and load power factor, as well as speeds, parameters and magnetising characteristics. Typical cases have been investigated for a number of test machines operating in parallel, and predictions of the proposed method have been verified experimentally.

DOI:10.1049/ip-c.1993.0007

出版商:IEE    

年代:1993

数据来源: IET

摘要:

A method of increasing the pulse number of an HVDC convertor based on the reinjection of the DC ripple is applied to a unit-connected generator-convertor scheme operating at variable speeds. Theoretical and experimental results are provided which demonstrate that, with the proposed modification, a single-bridge configuration can be made to operate as an 18-pulse convertor for a wide range of generator frequencies.

DOI:10.1049/ip-c.1993.0008

出版商:IEE    

年代:1993

数据来源: IET